ABO3 perovskite-type metal oxides such as lead zirconate titanate (referred to as “PZT” hereinafter) are typically used as piezoelectric materials. Since PZT contains lead as the A site element, a concern has been raised over PZT's impact on the environment. Thus, piezoelectric materials that use lead-free perovskite-type metal oxides are highly desirable.
An example of a lead-free piezoelectric material that contains a perovskite-type metal oxide is barium titanate. Studies on and development of barium-titanate-based materials been conducted to improve properties of barium titanate and devices that use such materials have been disclosed. PTL 1 discloses a piezoelectric element that uses barium titanate with the addition of Mn, Fe, or Cu and with some of the A sites being substituted with Ca. These piezoelectric elements have mechanical quality factors superior to those of barium titanate but have low piezoelectric properties. Thus, high voltage has been required to drive piezoelectric elements.
PTL 2 discloses an actuator and a liquid discharge head that use a material prepared by adding Ba and B to barium titanate. This material has an advantage of low sintering temperature but has a piezoelectric constant d33 as low as 65 [pC/N]. Thus, high voltage has been required to drive the piezoelectric element.
Piezoelectric materials having a Curie temperature of 80° C. or less may undergo depolarization in a severe environment such as car compartments under summer sun and may lose piezoelectricity as a result. Piezoelectricity may be lost by heat generated as a result of driving of actuators.